1. Field of the Invention
The present invention relates to a data recording and reproducing apparatus such as an AV server using a nonlinear accessible recording medium. The present invention relates also to a data recording and reproducing method for use in such data recording and reproducing apparatus.
2. Description of the Related Art
In recent years, as data are provided through multiple channels due to widespread CATV (cable television), etc. unlike a conventional VTR (video tape recorder), a demand for a variety of video tape recorder functions such as recording or reproducing a plurality of video/audio data (hereinafter referred to as “AV data”) simultaneously, or reproducing a plurality of AV data while recording the same by a single AV data recording and reproducing apparatus is increasing. To meet with such demand, devices called video server (or also called AV (Audio and/or Video) server) capable of recording and reproducing image/voice using a recording medium such as a hard disk which enables random access are being spread.
In general, AV servers for use in broadcasting stations need to have a required high data transfer rate and have a large storage capacity to record data for a long time from demands for high picture quality and high sound quality. An attempt has hitherto been made in order to increase a data transfer rate and a storage capacity by using a plurality of hard disk (hereinafter referred to as an “HD”) devices capable of storing AV data and processing in parallel. Further, another attempt has been made in order to keep servers highly reliable even if any of HD devices should break down by recording parity data.
This makes a multichannel AV server to be realized, which meets various uses such as constructing systems of VOD (video on demand) or NVOD (near video on demand),etc. by recording material data comprised of a plurality of AV data dispersedly for simultaneously transmitting them through multichannels or by reproducing the same material data through multichannels with staggered reproducing time, even though the number of required channels is different depending on contents of programs which the broadcasting station is to provide and the broadcasting format.
The HD devices for use in such AV server employ a RAID (Redundant Arrays of Inexpensive Disks) technique in which a plurality of hard disk drives (hereinafter referred to as “HDD”) comprising a plurality of HDs are arranged, which was proposed on a paper (‘A Case for Redundant Arrays of Inexpensive Disks (RAID)’, ACM SIGMOND Conference, Chicago, III, Jun. 1–3, 1988) presented by Patterson et al. in 1988.
In the above paper, the RAID is classified into five types from RAID-1 to RAID-5. RAID-1 is a system to write the same contents into two HDDs. RAID-3 is a system in which input data is recorded in a plurality of HDDs after the data is divided by the fixed length, and parity data that is exclusive-OR of corresponding data blocks of each HDD is generated and written into another HDD. RAID-5 is a system which increases the data division unit (block) to record one divided data as a data block in one HDD, records results of taking exclusive-OR of corresponding data blocks of each HDD (parity data) as parity blocks in other HDDs and disperses parity blocks to other HDDs.
Refer to the above paper for other RAIDs.
To record/reproduce a plurality of AV data by this AV server simultaneously, a video/audio signal (hereinafter referred to as an “AV signal”) has to be simultaneously inputted to and outputted through a plurality of channels. Therefore, the AV server includes a plurality of I/O ports which operate independently, and it is arranged that one input port and one output port inputs and outputs data for one channel, respectively.
However, when the respective I/O ports transfer AV data between them selves and a video recording and reproducing apparatus at the very same time, those AV data will simultaneously flow into buses connecting the respective I/O ports and the video recording and reproducing apparatus within the AV server, so that those data will be out of processing. Thus, time slots (=time intervals) for allowing the use of bus are allocated in turn to respective I/O ports and the respective I/O ports are arranged to transfer AV data between them selves and the video recording and reproducing apparatus in synchronism with a reference video signal through the bus during the allocated time slots only. Strictly speaking, although a plurality of AV data are not recorded/reproduced simultaneously, the simultaneous recording/reproducing of a plurality of AV data is sufficiently realized from the viewpoint of a time interval longer than the time slot.
FIG. 9 shows an example of an overall configuration of the conventional AV server. This AV server is a single body device in which a plurality of I/O processing sections 61 (three I/O processing sections 61a to 61c are shown in the figure), a plurality of RAIDs 62 (five RAIDs 62a to 62e are shown in the figure) and a time slot generating circuit 63 are housed in the same housing 66. The respective I/O processing sections 61 are connected to the respective RAIDs 62 through a down bus 64 and an up bus 65 arranged in the housing 66.
The time slot generating circuit 63 allocates in turn the time slots to the respective I/O processing sections 61 to permit them to use the buses 64 and 65 so as to prevent flowing of AV data from a plurality of I/O processing sections 61 to the bus 64 simultaneously or to prevent flowing of AV data to a plurality of I/O processing sections 61 to the bus 65 simultaneously.
When AVdata with a predetermined transmission format is inputted to any one of the I/O processing sections 61 from the outside of the AV server through a data input terminal Din, the I/O processing section 61 executes processing to convert the input data into data of the format recordable in the HD device (e.g. processing to derive AV data from the transmission format and processing to compress the derived data by MPEG or the like) and divides the AV data thus processed by the AV data to be recorded in the respective RAIDs 62 (e.g. divided by the frame). The divided data are transferred to the respective RAIDs 62 through the down bus 64 during the time slots allocated to the relevant I/O processing sections 61.
Additionally, the reason why the input data is not recorded in only one RAID 62 but is divided and recorded in each RAID 62 is that concentrated loads on a specific RAID 62 are avoided.
The respective RAIDs 62 are constructed using the RAID technique. Of the RAIDs 62, in the RAID using e,g, the RAID-3, AV data transferred from the I/O processing section 61 is divided by the definite length and recorded in a plurality of HDDs. At the same time, parity data is generated and recorded in another HDD.
On the other hand, when a reproduction request command is transferred from any of the I/O processing section 61 during the time slots allocated to that I/O processing section through the down bus 64 to the respective RAIDs 62, each of the RAIDs 62 reproduces AV data based on this command (e.g. the RAID using the RAID-3 reproduces divided AV data recorded in a plurality of HDDs. If a trouble occurs in any one of HDDs, then AV data of such HDD are restored using the parity data and those data are integrated). The reproduced AV data is transferred to the I/O processing sections 61 through the up bus 65 during the time slots allocated to that I/O processing sections 61.
The I/O processing section 61 performs a processing to convert AV data into data of a format that is transmissible to the outside (e.g. processing to expand compressed AV data and processing to convert expanded AV data into data of a predetermined transmission format). The AV data thus processed is outputted through a data output terminal Dout from the I/O processing section 61 to the outside of the AV server.
In this manner, each I/O processing section 61 inputs AV data for one channel and outputs AV data for one channel at the same time.
By the way, in the AV server designed as the single body device in which the I/O processing sections and the RAIDs are housed within the same housing as shown in FIG. 9, it is difficult to increase the RAIDs in order to enlarge the recording capacity after the AV server has been manufactured. In other words, this kind of AV server has low freedom of design due to restrictions on the physical structure.
In recent years, general-purpose computers (personal computers, workstations, etc.) becomes highly efficient and inexpensive increasingly and so such general-purpose computers should preferably be used as I/O processing section of AV server from the standpoint of costs. Nevertheless, the AV server in which the I/O processing sections and the RAIDs are held within the same housing as shown in FIG. 9 cannot use the general-purpose computer as its I/O processing section.
Thus, it is conceived to form the AV server itself not as the single body device which holds the I/O processing sections and the RAIDs within the same housing but as a system utilizing a network.
FIG. 10 shows a scheme of an AV server utilizing a network. A single or a plurality of I/O processing sections (three I/O processing sections 71a to 71c are shown in the figure) and a plurality of RAIDs 72 (five RAIDs 72a to 72e are shown in the figure) are connected to each other through a network 73.
When AV data of a predetermined transmission format is inputted to any of the I/O processing section 71 from the outside of the AV server, the I/O processing section 71 performs a processing to convert the AV data into data of a format recordable in the HD device, in the same way as in the I/O processing sections 61 shown in FIG. 9, divides the processed AV data by the AV data to be recorded in the respective RAIDs 72 and transfers the divided data through the network 73 to each RAID 72 together with a recording request command. The respective RAIDS 72 record AV data in the same way as the RAIDs 62 shown in FIG. 9 do so.
FIG. 11 shows AV data to be recorded in each RAID 72 when the I/O processing section 71 divides the AV data by the frame. The RAID 72a records F0, F5, F10, etc. which are AV data of 1st frame, 6th frame, 11th frame, and so on. The RAID 72b records F1, F6, F11, etc, which are AV data of 2nd frame, 7th frame, 12th frame, and so on, The RAID 72c records F2, F7, F12, etc. which are AV data of 3rd frame, 8th frame, 13th frame, and so on. The RAID 72d records F3, F8, F13, etc. which are AV data of 4th frame, 9th frame, 14th frame, and so on. The RAID 72e records F4, F9, F14, etc. which are AV data of 5th frame, 10th frame, 15th frame, and so on.
On the other hand, when a reproduction request command is transferred from any of the I/O processing section 71 through the network 73 to each RAID 72, each RAID 72 reproduces AV data based on this command similarly to the RAID 62 shown in FIG. 9. The reproduced AV data is transferred through the network 73 to the I/O processing section 71. The I/O processing section 71 converts the AV data into data of the format that is transmissible to the outside similarly to the I/O processing section 61 shown in FIG. 9. The AV data thus converted is outputted from the I/O processing section 71 to the outside of this AV server.
In this way, each I/O processing section 61 inputs AV data for one channel and outputs AV data for one channel at the same time.
Additionally, when recording request commands and reproducing request commands from a plurality of I/O processing sections 71 concur with each other, any one of the requests is given priority in accordance with a communication protocol of the network 73 or the order of priority is determined using a switch (not shown) which outputs selectively one of requests inputted thereto from the respective I/O processing sections 71. Accordingly, this AV server also may be assumed to transfer AV data between each I/O processing section 71 and the RAID 72 in a time-division manner.
Such AV server using the network can increase the recording capacity with ease by connecting a new RAID 72 to the network 73, so that a freedom of design will be enhanced. In addition, a general-purpose computer can be used as the I/O processing section and hence this server will be produced inexpensively.
However, the AV server utilizing the network involves a problem that need not be assumed with the AV server which holds the I/O processing sections and the RAIDs within the same housing. Specifically, for example, if a connector joining any RAID to the network is inadvertently separate and an operator of the I/O processing section is un aware of the separation of the connector from the network because the I/O processing section and the RAID are distant from each other, then the relevant RAID is unable to record and reproduce AV data. Accordingly, in reproduction, the AV server outputs AV data which lacks in data portion assigned to that RAID (e.g. if the RAID 72a is unable to record and reproduce AV data in FIG. 11, then AV data F0, F5, F10, etc. of 1st frame, 6th frame, 11th frame, etc. are lost. Consequently, when such AV data is transmitted as a broadcasting program, pictures and sounds are disturbed by noises or interruption.
Although this is not only a problem peculiar to the AV server utilizing the network but also a problem common to the AV server holding the I/O processing section and the RAID within the same housing, When one HDD within one RAID breaks down, data can be restored within the RAID, but when two or more HDDs within one RAID break down, data cannot be restored within the RAID and hence the relevant RAID is also unable to reproduce AV data. As a result, the AV server will output AV data which lacks in data portion assigned to that RAID. Further, when a CPU which controls the whole RAID breaks down within one RAID, the RAID is also unable to record and reproduce AV data, so that the AV server will output AV data which lacks in data portion assigned to that RAID.
In order to output AV data without loss even in such case, there is proposed a method of recording AV data double by back-up RAIDs provided in every RAID. According to this method, however, the number of RAIDs increases twice (ten RAIDs are required in the examples of FIGS. 9 and 10) and also a circuit for deciding which RAID is unable to record and reproduce data as well as a circuit for switching to the back-up RAID are required. Thus, the AV server will be large in scale. Moreover, if AV data is recorded double in the AV server utilizing the network, an amount of data transferred over the network increases twice and so a load imposed upon the network also increases.